JPH11279710A - Bearing steel excellent in acoustic property and quietness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel excellent in an acoustic property and quietness by making an acid insoluble impurity less than a specified pieces per unit steel when dissolving, in a mixed acid aqueous solution heated to a specified temp, the steel which contains a specified content in each of C, Si, Mn, Cr, Al and the balance Fe with inevitable impurities, and restricts Ti, O in the impurities to a specified content. SOLUTION: A content, by weight, is 0.6-1.2% C, 0.1-2.0% Si, 0.1-2.0% Mn, 10.0-14.0% Cr, <=0.04% Al. Ti, O in the impurities, by weight, <=0.0015% T, <=0.0012% O. A mixed acid aqueous solution is prepared by mixing, by mass, 60% nitric acid, 96% sulfuric acid, pure water in the volume ratio of 25:1:55 and heating to 90-95 deg.C. An acid insuluble impurity includes Al2 O3 of 50%, and its size is >=15 μm major diameter and is less than 19 pieces in 10 g of the steel. In the case corrosion resistance is not required, a Cr content is 0.8-2.0%, and in the case of needing that of medium degree, it is 2.0-10.0%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention requires a bearing material used for a rolling bearing such as a roller bearing or a ball bearing, particularly an air conditioner, a disk drive of a computer, a video and audio equipment, etc., which require acoustic characteristics and quietness. It relates to the most suitable bearing steel for use in precision equipment.

[0002]

2. Description of the Related Art The term "acoustic characteristics and quietness" as used herein refers to a level of noise generated by vibrations generated during the operation of rolling bearings and other rolling devices, and is a serious problem in machine tools and construction machines. No, for example, HDD or VTR
In relatively small ball bearings and the like used in precision equipment that extremely dislikes vibrations, acoustic characteristics and quietness are serious problems. In these small ball bearings, since the applied load is not so large, fatigue characteristics such as rolling fatigue life are not regarded as much problems, and quietness and acoustic characteristics during rotation are regarded as important. It has been done.

[0003] By the way, two types of attention are paid to the acoustic characteristics and quietness of the bearing steel: an acoustic characteristic at the beginning of use and deterioration of the acoustic characteristics due to aging during use. First, the acoustic characteristics in the initial stage of use largely depend on the finishing accuracy of the shape of the bearing component. In terms of material, the finishing accuracy is greatly affected by the number and size of non-metallic inclusions and eutectic carbides whose hardness differs greatly from that of the matrix. In addition, as for the acoustic characteristics due to aging during use, even when the acoustic characteristics in the initial stage of use have no problem, they occur between the base and hard nonmetallic inclusions or eutectic carbides during use of the bearing parts. The difference in wear leads to deterioration of accuracy such as surface shape and surface roughness, and lowers acoustic characteristics during use. Among them, the eutectic carbides are disclosed in Japanese Patent Application Laid-Open No. 61-163244 with respect to the size and amount limits.

[0004] On the other hand, it is generally known that nonmetallic inclusions are harmful to various characteristics (for example, rolling fatigue life) of bearing parts. Many have been disclosed in which is controlled low. As a means for reducing non-metallic inclusions, O, Ti
In the prior art, which is controlled to be low, focusing on the rolling fatigue life of a bearing or a rolling part, and focusing on quietness and acoustic characteristics, the size of nonmetallic inclusions is reduced. It has not been studied in terms of number, number, existence probability, etc. Therefore, the relationship between quietness and acoustic characteristics and the size and number of nonmetallic inclusions has not been clarified at all.

[0005]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 61-16 / 1986
Japanese Unexamined Patent Publication No. 3244 discloses a limit on the size and amount of eutectic carbide which greatly affects the finishing accuracy of the shape of a bearing component.
In the case of C: 0.6 to 1.2% and Cr: 0.8 to 14.0%, eutectic carbides are developed due to the development of manufacturing methods such as controlling the size of the steel ingot and performing soaking. Has a relatively small effect on the acoustic characteristics. In addition, it did not focus on the number and size of nonmetallic inclusions.

[0006] The shape finishing accuracy of the bearing component greatly affects the number and size of the non-metallic inclusions which are not considered in the present invention, that is, the number and size of the non-metallic inclusions are large and large as compared with the eutectic carbide, and the number of the non-metallic inclusions is large in the manufacturing process. Al ₂ O difficult to control
₃ The size and number of hard oxide-based inclusions having a content of 50% or more.

[0007] When a bearing oxide steel containing a large number of hard oxide inclusions having an Al ₂ O ₃ content of 50% or more is used as a material for a bearing component, the coarse and hard steel is used. Non-metallic inclusions appear on the surface of the rolling device component, deteriorating the finishing accuracy and deteriorating the acoustic characteristics.
In addition, a difference in abrasion generated between the base and the hard nonmetallic inclusion during use causes deterioration in accuracy of the surface shape, and causes deterioration in acoustic characteristics due to aging. On the contrary, the present inventors have found that the acoustic characteristics at the beginning of use can be improved by accurately grasping and controlling the size, number, and abundance ratio of the hard oxide-based inclusions.

The present invention has been made in view of the above-mentioned conventional circumstances, and is capable of accurately and quantitatively detecting hard oxide-based nonmetallic inclusions that adversely affect acoustic characteristics and quietness. It is an object of the present invention to provide a bearing steel capable of controlling the number and size thereof using a grasping method, and thereby obtaining stable acoustic characteristics and quietness.

[0009]

The bearing steel excellent in acoustic characteristics and quietness according to the present invention, which can achieve the above object, is expressed in terms of% by weight, C: 0.6 to 1.2%. , Si: 0.
1 to 2.0%, Mn: 0.1 to 2.0%, Cr: 0.8
１４14.0%, Al: 0.04% or less, the balance being Fe and unavoidable impurities.
0015% or less, O: a steel material suppressed to 0.0012% or less, respectively, and 60% heated to 90 to 95 ° C.
When the steel material is dissolved in a mixed acid aqueous solution (mean% by mass: the same applies hereinafter) of nitric acid, 96% sulfuric acid, and pure water having a volume ratio of 25: 1: 55, the long diameter is 15 μm or more. This is characterized in that the number of acid-insoluble inclusions having an Al ₂ O ₃ content of 50% or more is less than 10 per 10 g of the steel material.

In the above steel material, Cr is 10.0 to 1% by weight in consideration of corrosion resistance, hardness, cost and the like.
4.0%, 2.0-10.0%, 0.8-2.0%
Are divided into ranges. If necessary, Ni: 0.1 to
2.0%, Cu: 0.1-1.0%, Mo: 0.1-
2.0%, W: 0.1-1.0%, V: 0.05-1.
By containing one or more selected from 0% and Nb: 0.01 to 1.0%, the performance can be further improved.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention has the greatest influence on the quietness and acoustic characteristics as a factor of the material (steel material in the present invention) of a bearing component, and it is difficult to control the Al in the steel material manufacturing process.
It is a steel material in which the size, number, and abundance ratio of hard oxide-based inclusions having a ₂ O ₃ content of 50% or more are accurately grasped and controlled, and preferred basic components are as follows.

The content of C is% by weight (hereinafter the same),
0.6 to 1.2%. C is an element essential for increasing quenching hardness, maintaining strength at room temperature and high temperature, and imparting wear resistance. When the content is less than 0.6%, the quenching hardness is insufficient and the wear resistance cannot be maintained. On the other hand, if it exceeds 1.2%, a giant eutectic carbide which cannot be diffused even by soaking for a long time is generated, and therefore, the grindability, cold forgeability, and machinability are reduced, including the quietness of the bearing component. .

Further, the content of Si is set to 0.1 to 2.0%. This Si is an element necessary for deoxidation in the steel making process, and has an effect of increasing wear resistance and strength. At least 0.1% is necessary. However, if the content exceeds 2.0%, the cold forgeability and machinability deteriorate, so the content is set to 0.1 to 2.0%.

[0014] The Mn content is 0.1 to 2.0%.
This Mn improves the hardenability to increase the strength, but if it is too much, it increases the retained austenite, conversely lowers the strength and causes aging of the dimensions. Therefore, the component range is set to 0.1 to 2.0%.

The content of Cr is. 10.0 ~
14.0%,. 2.0-10.0%,. 0.8 ~
It is classified into the range of 2.0%. Cr is a particularly important element, and improves corrosion resistance and heat resistance while improving strength and hardenability. In addition, Cr forms fine carbides in combination with C to provide wear resistance. However, if the Cr content is less than 0.8%, the effect is not obtained. If the Cr content exceeds 14.0%, a huge eutectic carbide is generated.
4.0%.

Here, in the range of Cr: 0.8 to 14.0%, the corrosion resistance changes as shown in FIG. 1 as its content increases. In the case of bearing components, the required corrosion resistance varies greatly depending on the application. In the case where corrosion resistance is not required in ordinary applications, the Cr content is sufficient at 0.8 to 2.0%, and the role of Cr in this case is to improve strength and hardenability. However, in applications where sufficient corrosion resistance is required, such as bearing parts that are completely degreased during assembly, such as ball bearings for HDDs, and are susceptible to rust, and portable precision equipment used in coastal areas. , Cr content is at least 1
0.0% is required, and the range is 10.0 to 14.0%. In the intermediate range of 2.0 to 10.0%, the amount of Cr is selected according to the corrosion resistance required for each use of the bearing component. If a large amount of Cr is contained, the production cost naturally increases in proportion to the content. Therefore, the range of the Cr component should be selected according to the required corrosion resistance and cost.

The content of Al is set to 0.040% or less. This Al is an indispensable element for deoxidation in the steel making process, and in particular, a certain amount of addition is necessary to reduce O to 0.0012% or less. However, if contained in a large amount, a large amount of hard oxide-based inclusions having a high Al ₂ O ₃ content is generated, so the upper limit is made 0.040%.

The above are the basic components of the steel material according to the present invention. Next, Ti and O among the inevitable impurities will be limited as follows. That is, the content of Ti is set to 0.0015% or less. This Ti is preferably low because it forms hard non-metallic inclusions TiN and degrades quietness and acoustic characteristics, but it is allowable up to 0.0015%. Therefore, the upper limit is made 0.0015%.

The content of O is set to 0.0012% or less. O is preferably low because it forms hard oxide-based nonmetallic inclusions and degrades quietness and acoustic characteristics.
Up to 0.0012% is acceptable. Therefore, the upper limit is set to 0.
0012%. However, as described above, when the O content is 0.0012% or less, no clear correlation is observed between the O content and the number of oxide-based inclusions. Therefore, quietness,
The number of hard oxide-based nonmetallic inclusions having a major axis of 15 μm or more harmful to acoustic characteristics and an Al ₂ O ₃ content of 50% or more is separately specified by designating an optimum measurement method.

Here, the amounts of O and Ti, the number of nonmetallic inclusions,
Regarding the relationship with the size, the inclusions of Ti are arranged in a relatively simple relationship since the generated inclusions are almost limited to TiN, and there is a certain correlation between the amount of Ti and the number and size of the Ti-based nonmetallic inclusions. , Ti can be estimated to some extent from the analysis values of Ti. On the other hand, O combines with Al, Si, Ca, Mg, Mn, etc. to generate various kinds of nonmetallic inclusions, and slag is involved in oxide-based inclusions, and is melted in the steel making process. Includes refractories.

Therefore, in a highly clean steel having an O content of 0.0012% or less, there is almost no correlation between the O content and the number and size of nonmetallic inclusions. This has been described in the literature (Materials and Processes, 4 (1991), 1178, Materials and Processes,
4 (1991), 321). Therefore, the only method of evaluating nonmetallic inclusions in bearing steel is to directly measure the number and size of the nonmetallic inclusions using an optimal method.

Conventional methods for measuring non-metallic inclusions include a method of observing the L section (longitudinal longitudinal section) of a steel material with a microscope and examining the number, size, and length of inclusions present in the section. This method is generally used and is described in JIS G 055.
5 and ASTM E-45. But,
The observation of the L cross section of a steel material is an evaluation of inclusions existing in only a limited cross section. In addition, in the observation of a cross section of a steel material, the probability of measuring the maximum diameter of each nonmetallic inclusion is extremely high. Due to the small size, it is difficult to perform accurate evaluation in observation with a limited area.

In particular, when the O content is 0.0012% or less, the accuracy of observation of a cross section of a steel material is limited because the existence probability of oxide-based nonmetallic inclusions decreases. In addition, a harmful Al ₂ O ₃ content of 50% among many kinds of oxide-based nonmetallic inclusions.
% Of hard inclusions was difficult to identify. Here, Japanese Unexamined Patent Publication (Kokai) No. 3-126839 discloses that inclusions in bearing steel are guaranteed by an electron beam melting and extraction evaluation method. However, this is a measurement of nonmetallic inclusions with a focus on rolling fatigue life, and does not examine the relationship between quietness and acoustic characteristics. In this electron beam melting and extraction evaluation method, a sample is melted by an electron beam to float nonmetallic inclusions having a low specific gravity.

Therefore, in this electron beam dissolution extraction evaluation method, the sample must be completely dissolved, and in the case of non-metallic inclusions having a low melting point (having a melting point close to the melting point of steel), the sample must be completely dissolved. Measurement is impossible. Even non-metallic inclusions that do not re-dissolve are difficult to completely float while maintaining their original shape due to high temperatures, and are likely to be observed in larger sizes due to aggregation and sintering. High measurements were difficult.

Therefore, in the measurement of nonmetallic inclusions in the present invention, the volume ratio of 60% (mean% by mass; the same applies hereinafter) nitric acid, 96% sulfuric acid, and pure water heated to 90 to 95 ° C. A steel material is dissolved in a 25: 1: 55 mixed acid aqueous solution,
By adopting a method in which acid-insoluble inclusions are subjected to EPMA analysis to measure the Al ₂ O ₃ concentration, major axis and number thereof,
Experimental data as shown in FIG. 2 could be obtained.

The steel material according to the present invention can further contain the following component elements, if necessary. That is,
The content of Ni is set to 0.1 to 2.0%. This Ni is added as needed in the present invention. Addition of 0.1% or more has the effect of improving the hardenability and increasing the hardening effect depth, and at the same time, has the effect of improving the toughness and ductility. If contained in a large amount, the retained austenite increases, causing aging during the use of the bearing component and deteriorating the acoustic characteristics. Therefore, the upper limit is made 2.0%.

The content of Cu is 0.1 to 1.0%.
Cu is added as necessary in the present invention. 0.1%
Addition of the above improves hardenability and corrosion resistance. If it is contained in a large amount, red hot brittleness is promoted and hot workability is deteriorated, so the upper limit is made 1.0%. The content of Mo is 0.1 to
2.0%. This Mo is added as needed in the present invention. Addition of 0.1% or more improves hardenability and corrosion resistance and wear resistance. When added in an amount of 2.0% or more, a large amount of M ₆ C carbides is generated, the effect of addition is saturated, and the upper limit is set to 2.0% in order to degrade quietness and acoustic characteristics.

The content of W is 0.1-1.0%. This W is added as needed in the present invention. The effect is the same as Mo. Since the effect is saturated at 1.0%,
The upper limit is set to 1.0%. And the content of V is 0.05
To 1.0%. V is added as needed in the present invention. When added in an amount of 0.05% or more, fine VC carbides are formed, and the crystal grain size is reduced, and the wear resistance and heat resistance are improved. However, if added in an amount of 1.0% or more, the VC carbides become coarse and the quietness and acoustic characteristics deteriorate, so the upper limit is made 1.0%.

The content of Nb is 0.01 to 1.0%. Nb is added as needed in the present invention.
By adding 0.01% or more, fine NbC carbides are generated to refine the crystal grain size. If more than 1.0% is added, NbC
The upper limit is set to 1.0% because carbides are coarsened and the silence and acoustic characteristics are deteriorated.

[0030]

EXAMPLES Next, in order to specifically explain the present invention with reference to Examples and Comparative Examples, Table 1 shows the chemical compositions of the steel materials of the present invention and comparative steel materials. The steel material tested was obtained by subjecting molten steel to refining and degassing, and then forming an ingot, followed by hot rolling into a rod having a diameter of 25 mm and a wire having a diameter of 5.5 mm. N in Table 1
0.1 to N0.19 are steel materials of the present invention, and N0.20 to N0.19.
N0.24 is a conventional steel material.

[0031]

[Table 1]

Table 2 shows the measurement results of the acid-insoluble inclusions in the steel material of the present invention and the comparative steel material, heat treatment conditions, and various properties after the heat treatment. The measurement of the acid-insoluble inclusions is performed by removing the surface scale of the wire, heating 60% to 90 ° C to 95 ° C (mean% by mass: the same applies hereinafter) nitric acid,
The test steel was dissolved in a mixed acid aqueous solution of 96% sulfuric acid and pure water at a volume ratio of 25: 1: 55.

[0033]

[Table 2]

After dissolving the steel material, it was subjected to suction filtration with a filter having a sieve of 5 μm, and then washed with pure water, dilute hydrochloric acid and ethanol using a filter having a sieve of 1 μm. After washing, the filter from which the acid-insoluble inclusions were collected was dried, and non-metallic inclusions on the filter were analyzed by EPMA, and the Al ₂ O ₃ concentration, major axis, and number were measured. FIG. 2 shows the measured values in a graph.

As for the eutectic carbide, the L section (longitudinal section in the longitudinal direction) of the steel material was observed with an optical microscope at 330 mm ² , and it was confirmed whether or not there was one having a major axis of 15 μm or more.
As for the corrosion resistance, a pure water spray test was conducted for 200 hours.
The salt spray test of Hr and 5% NaCl was performed for 3 hours,
Five-stage evaluation of 1 to 5 points was visually performed. FIG. 1 shows the measured values in a graph. The best score is 5 points.

Further, regarding the quietness and acoustic characteristics, the inner and outer rings of the ball bearing were manufactured from the test materials, and the balls made of SUJ2 were incorporated into the AFBMA (The Anti-Friction Bearing M).
anderon values measured in accordance with the standards of the Anufacturers Association, Inc.
z) and a high frequency band (1800 to 10000 Hz). The values shown in Table 2 correspond to the values of sample N
It was indicated by an index using 0.20 (conventional steel) as a reference (100).

The numerical value of the steel material of the present invention is smaller than that of the conventional steel material in both the middle frequency band and the high frequency band, indicating that the steel material is excellent in quietness. FIG. 3 is a diagram showing the number of nonmetallic inclusions and an index of quietness shown in Table 2 of the steel material of the present invention.

[0038]

As described above, the bearing steel according to the present invention is characterized in that the size and number of hard oxide-based inclusions having an Al ₂ O ₃ content of 50% or more, which are difficult to control in the steel material manufacturing process,
Because it is a configuration in which the number of existence is accurately grasped and controlled, silence and acoustic characteristics can be stably set to a good level, and silence and acoustic characteristics that are important issues with precision equipment In addition, there is an effect that a small-sized rolling bearing having excellent characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between Cr content and corrosion resistance.

FIG. 2 is a graph showing the relationship between the amount of O and the number of acid-insoluble inclusions having an Al ₂ O ₃ content of 50% or more.

FIG. 3 is a graph showing a relationship between the number of acid-insoluble inclusions having an Al ₂ O ₃ content of 50% or more and a quietness index.

[Table 1]

[Table 2]

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koji Kaneki 1 Kanazawacho, Kakogawa-shi, Hyogo Kobe Steel Works Kakogawa Works

Claims (4)

[Claims] 1. C .: 0.6 to 1.2% by weight, S
i: 0.1 to 2.0%, Mn: 0.1 to 2.0%, C
r: 10.0 to 14.0%, Al: 0.04% or less, balance consists of Fe and unavoidable impurities. Ti: 0.0015% or less and O: 0.0012% or less in the inevitable impurities. A 60% (mean% by mass: the same applies hereinafter) nitric acid heated to 90 to 95 ° C.,
When the steel material is dissolved in a mixed acid aqueous solution of 96% sulfuric acid and pure water having a volume ratio of 25: 1: 55, an acid having a major axis of 15 μm or more and an Al ₂ O ₃ content of 50% or more is used. A bearing steel having excellent acoustic characteristics and quietness, characterized in that the number of insoluble inclusions is less than 10 per 10 g of the steel material. 2. C: 0.6 to 1.2% by weight, S
i: 0.1 to 2.0%, Mn: 0.1 to 2.0%, C
r: 2.0 to 10.0%, Al: 0.04% or less, the balance is composed of Fe and unavoidable impurities, and Ti is 0.0015% or less and O: 0.0012% or less in the unavoidable impurities. Of 60% (mean% by mass; the same applies hereinafter) nitric acid heated to 90 to 95 ° C., 9
When the steel material is dissolved in a mixed acid aqueous solution of 6% sulfuric acid and pure water having a volume ratio of 25: 1: 55, an acid having a major axis of 15 μm or more and an Al ₂ O ₃ content of 50% or more is used. A bearing steel having excellent acoustic characteristics and quietness, characterized in that the number of insoluble inclusions is less than 10 per 10 g of the steel material. 3. C: 0.6-1.2% by weight, S
i: 0.1 to 2.0%, Mn: 0.1 to 2.0%, C
r: 0.8 to 2.0%, Al: 0.04% or less, the balance being Fe and unavoidable impurities.
i: a steel material suppressed to 0.0015% or less and O: 0.0012% or less, and 60% (mean% by mass: the same applies hereinafter) nitric acid heated to 90 to 95 ° C., 96
% Sulfuric acid, pure water having a volume ratio of 25: 1: 55 when the steel material is dissolved in an aqueous solution of an acid, and having a major axis of 15 μm or more and an Al ₂ O ₃ content of 50% or more. A bearing steel having excellent acoustic characteristics and quietness, characterized in that the number of inclusions is less than 10 per 10 g of the steel material. 4. Ni: 0.1 to 2.0% by weight, C:
u: 0.1 to 1.0%, Mo: 0.1 to 2.0%, W:
0.1-1.0%, V: 0.05-1.0%, Nb:
4. The bearing steel according to claim 1, wherein said steel is one or two or more of 0.01 to 1.0%.